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What is killing bald eagles in the United States?

Written by Martin Luther, University of Haley-Wittenberg

Bald eagles, as well as other wildlife, have been subject to a mysterious neurodegenerative disease in the southern United States since the 1990s. New research by Martin Luther Hall-Wittenberg (MLU) in Germany and the University of Georgia, USA, has identified the cause of these deaths: the toxin produced by cyanobacteria that grow on invasive aquatic plants. The problem is likely to be exacerbated by the use of herbicides to control these plants. The results have been published in Science.

In 1994, They were dying out on a large scale in the US state of Arkansas. The animals were losing control of their bodies, and holes were developing in their brains. A previously unknown neurodegenerative disease called myeloid myelopathy (VM) has been identified. “The origin of the disease was a mystery,” says Professor Timo Niedermeier of MLU’s Institute of Pharmacy.

Bacterial colonies of cyanobacteria A. hydrillicola grow on the leaf of the invasive aquatic plants H. verticillata. Credit: Susan Wilde

Later, American researchers found that not only vultures were affected, but also their herbivorous prey. Scientists have discovered a link to an invasive aquatic plant (Hydrilla verticillata) growing in freshwater lakes in affected areas. However, there are still lakes with aquatic vegetation where disease does not appear. In 2005, Susan B. Wilde, a professor at the Warnell School of Forest and Natural Resources at the University of Georgia, identified a previously unknown blue bacterium on the leaves of Hydrilla verticillata, which appears to be the cause of the disease. It turns out that myelopathy occurs only in places where cyanobacteria colonize the invading plant. I called the bacteria the “killer eagle that grows on Hydrilla”: Aetokthonos hydrillicola.

“I stumbled across a press release from the university in Georgia and was astonished by these results, because I’ve worked with cyanobacteria for years,” says Niedermeier. Samples were sent to him and the bacteria were grown in the laboratory and returned to the United States for further testing. But the results were negative: the bacteria from the laboratory did not cause the disease. “It wasn’t just the birds that went crazy, we were, too. We wanted to find out,” Niedermeier says. Once again, send him colony papers. Then Steffen Breinlinger, a doctoral student in his research group, used a new mass spectrometry scale to examine the structure on the surface of a plant leaf, molecule by molecule. He discovered a new substance that only occurs in the leaves where cyanobacteria grow, but is not produced in the cultivated bacteria.

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His investigations of the chemical composition of the isolated molecule showed that it contained five bromine atoms. “The structure is really amazing,” says Brenlinger. The properties are unusual for the molecule that bacteria form. They provide an explanation of why the toxin did not form under laboratory conditions. The standard culture media in which cyanobacteria grow do not contain bromide. “Then we added bromide to our laboratory cultures, and the bacteria started producing the toxin,” Brenlinger says. Wilde and colleagues tested the isolated molecule in birds, and finally, after nearly a decade of research in Wild and Niedermeer’s labs, they had the evidence: the molecule induces VM activation. According to the bacterium’s name, researchers call their discovery aitokthonotoxin, “the vulture-killing poison.” “Finally, not only did we catch the killer, but we also identified the weapon the bacteria used to kill those vultures,” says Wilde.

A research group participating in the study from the Czech Academy of Sciences also found sections of DNA that contain genetic information for the synthesis of the new molecule. Why are cyanobacteria poisoning in aquatic organisms In the first place, however, it has not yet been studied. One of the herbicides used to control invasive aquatic plants may play an important role in the occurrence of VM: it contains bromide and thus may stimulate toxin production.

Nervousness It has not yet occurred in Europe, and no case of toxin-forming cyanobacteria has been reported.

Newspaper article

Top image: Pixabay


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